Resolve "Move EE-specific images to `ee/app/assets/images` directory"

What does this MR do?

› git diff ce/master..origin/master --name-status ./app/assets/images | grep -e '^A' | cut -f2 | xargs -t -L1 -I % dirname % | xargs -t -L1 -I % mkdir -p ee/%

dirname app/assets/images/authbuttons/kerberos_32.png
mkdir -p ee/app/assets/images/authbuttons
dirname app/assets/images/authbuttons/kerberos_64.png
dirname app/assets/images/favicon-green.ico
mkdir -p ee/app/assets/images/authbuttons
dirname app/assets/images/gitlab_for_slack.gif
mkdir -p ee/app/assets/images
mkdir -p ee/app/assets/images
dirname app/assets/images/illustrations/gitlab_geo.svg
dirname app/assets/images/mailers/approval/icon-merge-request-gray.gif
mkdir -p ee/app/assets/images/illustrations
dirname app/assets/images/mailers/approval/icon-x-orange-inverted.gif
mkdir -p ee/app/assets/images/mailers/approval
mkdir -p ee/app/assets/images/mailers/approval

and then

› git diff ce/master..origin/master --name-status ./app/assets/images | grep -e '^A' | cut -f2 | xargs -t -L1 -I % git mv % ee/%                                  

mv app/assets/images/authbuttons/kerberos_32.png ee/app/assets/images/authbuttons/kerberos_32.png
mv app/assets/images/authbuttons/kerberos_64.png ee/app/assets/images/authbuttons/kerberos_64.png
mv app/assets/images/favicon-green.ico ee/app/assets/images/favicon-green.ico
mv app/assets/images/gitlab_for_slack.gif ee/app/assets/images/gitlab_for_slack.gif
mv app/assets/images/illustrations/gitlab_geo.svg ee/app/assets/images/illustrations/gitlab_geo.svg
mv app/assets/images/mailers/approval/icon-merge-request-gray.gif ee/app/assets/images/mailers/approval/icon-merge-request-gray.gif
mv app/assets/images/mailers/approval/icon-x-orange-inverted.gif ee/app/assets/images/mailers/approval/icon-x-orange-inverted.gif

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan

What are the relevant issue numbers?

Closes #4630 (closed)